This invention relates to novel organic extractants for removing cobalt and nickel values from aqueous solutions.
It is known that nickel can be recovered from its concentrated acidic solutions by electrowinning. However, if the nickel solution is ammoniacal, or if the solution is too dilute, then the nickel ions must be extracted by liquid ion exchange and back extracted into a sulfuric acid solution before being electrowon. The purity of the nickel obtained from such a process is very sensitive to the nature and concentration of the impurities present in the solution.
It is also known that nickel can be obtained from its solutions by hydrogen reduction at elevated temperatures and pressures. Typically, nickel won by this method is very impure.
Because of the difficulties of the foregoing nickel recovery processes, carbonylation processes for recovering nickel and cobalt have recently been developed. In the carbonylation process, very pure nickel and cobalt of acceptable purity are obtained by treating nickel and cobalt values to produce carbonyl compounds. The gaseous compound Ni(CO).sub.4 is then isolated and thermally decomposed to yield pure metal pellets and carbon monoxide gas. The purity of the nickel metal produced by this process is excellent because of the selectivity of the carbonylation reaction and because other metals often present with nickel do not form gaseous compounds.